[PR #12101/e458a830 backport][3.14] Strip function def from code example (#12103)

**This is a backport of PR #12101 as merged into master
(e458a83).**

Author: patchback[bot]

docs/client_middleware_cookbook.rst

@@ -60,6 +60,8 @@ efficient to implement without a middleware:
 
 .. literalinclude:: code/client_middleware_cookbook.py
    :pyobject: token_refresh_preemptively_example
+   :lines: 2-
+   :dedent:
 
 Or combine the above approaches to create a more robust solution.